This invention relates generally to charge transfer devices; and, more particularly, to an apparatus and a method for regenerating charge packets representing information in a semiconductor charge transfer device.
A component utilized in some practical applications of charge transfer devices is a charge regenerator. The regenerator is used to reduce deviations from the correct amount of charge in a charge packet representing either a logical 1 or a logical 0. Without regeneration the amount of charge in a packet representing a logical 1 and the amount of charge in a packet representing a logical 0 tend to equalize, making discrimination between the two more difficult and eventually resulting in a loss of information.
Known prior art methods typically have used a threshold or reference voltage in a charge regenerator. Such a regenerator is described by M. F. Tompsett in an article entitled "A Simple Charge Regenerator for Use with Charge Transfer Devices and the Design of Functional Logic Arrays," appearing in the IEEE Journal of Solid State Circuits, June, 1972, page 237. In the described regenerator the flow of charge carriers from a charge source is controlled by a potential barrier whose level is a function of the charge to be regenerated. A threshold or reference voltage is applied to the charge carrier source. The voltage is set to a potential level between the level of the potential barrier representing a logical 1. and the level of the potential barrier representing a logical 0. Therefore, charge flows from the source when there is a potential barrier representing a logical 0 and does not flow when there is a potential barrier representing a logical 1.
As the overall transfer efficiency approaches 50 percent, the separation between the potential level representing a logical 1 and the potential level representing a logical 0 diminishes and the requirements on the stability of the reference voltage becomes severe. The reference voltage is often derived using an on-chip voltage regulator which depends upon the difficult-to-control threshold voltages of insulated gate field effect transistors. Also, regeneration as taught in the Tompsett article results in an inversion of logical 1--s and 0+s. It would be desirable to eliminate the need for a threshold voltage and its associated voltage regulator. It would further be desirable to regenerate charge packets representing information without inverting.
Other prior art teaches performing various arithmetic and logic functions using charge transfer devices. For example, U.S. Pat. No. 3,777,186, issued to W. H. Chang on Dec. 4, 1973 and an article by T. D. Mok and C. A. T. Salama entitled "Logic Array Using Charge Transfer Devices" appearing in Electronics Letters, Vol. 8, No. 20, Oct. 5, 1972, page 495, describe performing logic functions using charge transfer devices. The logic functions are obtained by using parallel and serial gates to perform operations akin to charge limitation and charge subtraction. However, it is neither taught nor suggested that such techniques can be used to regenerate charge in charge transfer devices.